In general, fabric filters are designed to provide fibers (pile threads) on one surface of a disk-shaped filter, and to filtrate foreign materials when a pollutant such as polluted water passes through the disk-shaped filter.
Such a disk-shaped fabric filter is disclosed in Korean Patent No. 10-0424226 (Mar. 11, 2004). This filter is a filtering device for liquid filtration in which: a filter cloth is placed on a flow path of liquid to be filtrated and has pile threads 21 on its side exposed to a flow of the liquid; the length, strength and density of the pile threads are so calculated that the pile threads are laid flat by the flow of the liquid to be filtrated and form a deep filter with a plurality of angular, meandering flow passages; the filter cloth includes a suction bar 13 that has a suction slit 17 across the side of the filter cloth and suctions a back-washing flow through the filter cloth at a flow rate at which the pile threads are straightened so as to stand straight from the filter cloth when back-washed, and means for relatively moving the suction bar relative to the filter cloth 6 in a moving direction parallel to the filter cloth; the suction bar 13 at least has a surface 18 directed to the filter cloth 6 on the side of the suction slit 17 located in the front thereof with respect to the relative movement; and the surface faces the filter cloth 6 with a narrow gap and thus prevents the pile threads from being straightened by a mechanical action applied to the pile threads.
Particularly, this filtering device performs a back-washing action in which, as a disk-shaped filter piece 5 rotates with the suction bar 13 fixed, the straightening is delayed by the surface 18 of the suction bar 13 before the pile threads 21 reach the suction slit 17, and then is rapidly made when the pile threads 21 reach the suction slit 17, so that foreign materials trapped by the pile threads 21 in the filtration process are suctioned toward the suction bar 13.
However, this convention filtering device has a limitation of the back-washing effect, because the straightening of the pile threads is simply delayed by the surface 18 of the suction bar 13.